Novel polyamine compounds and their use as curing agents for epoxy resins

ABSTRACT

Disclosed are novel polyamine compounds having the general formula ##STR1## wherein R, R 1 , R 2  and R 3  are each independently selected from hydrogen and alkyl groups which may be substituted, the preparation of such compounds and their use as curing agents for epoxy resins.

This is a division of application Ser. No. 301,919, filed Sept. 14,1981.

This invention relates to polyamine compounds and to their preparationand use. The compounds have the general formula ##STR2## wherein R, R¹,R² and R³ are each independently selected from hydrogen and straight orbranched chain alkyl groups of 1 to 10, preferably 1 to 6, and mostpreferably 1 to 3 carbons which may be substituted with 1-3 of the sameor different groups selected from alkoxy of 1-10 carbons, phenyl,cyclohexyl and hydroxyl. These compounds are particularly effective ascuring agents for epoxy resins.

It is known that polyepoxides may be cured with a variety of amines suchas pyridine, piperidine, diethylenetriamine, meta-phenylene diamine,bis(1-aminocycloalkylmethyl)amines, and ethylenediamine. The use of suchamines has not been satisfactory in certain commercial applications fora number of reasons. For example, such amines can be quite volatile andgenerate noxious fumes during and after curing which causes irritationof the eyes and skin, they can be difficult to blend with epoxy resinsand fail to give products having sufficient hardness and strength,especially at elevated temperatures, and frequently they can impart poorpot life to the resin as well as unsatisfactory colour to the curedproduct.

It has been found that the polyamines of the above general formula areexcellent curing agents for a broad range of epoxy resins, impartingmuch improved properties thereto without the aforementioned drawbacks.These polyamines can be produced readily by reacting epichlorohydrinwith a diamine or diamines of the formula ##STR3## wherein A and B,which may be the same or different, are selected from R, R¹, R² and R³as defined above. The reaction is preferably carried out in a suitablesolvent in the presence of an acid scavenger at concentrationspreferably approaching theoretical, at temperatures between the freezingand boiling point of the reaction mixture, and in an open or closedreactor at pressures ranging from subatmospheric to superatmospheric.

The molar ratio of the diamine to epichlorohydrin can vary widely, butis preferably within the range from 2/1 to 5/1, and most preferablybetween 2 to 2.2/1. It is possible to carry out the reaction in theabsence of either or both of HCl scavenger and solvent, but the reactionwould take an excessive period of time to complete and would requirerigorous agitation to ensure even dispersion of the reactive materials.It is preferred, therefore, that a suitable base such as sodiumhydroxide be used and that the reactive materials be dispersed in asuitable solvent such as water and/or an alcohol of from 2 to 6 carbonssuch as methanol, ethanol, butanol or propanol. A mixture of methanoland water with a preponderant proportion of methanol is a preferredsolvent. The base is added as necessary to reduce the HCl level, and canbe of any type including alkali or alkaline earth hydroxides, andamines, as long as it is selected from those bases which do not enterinto or adversely affect the principal reaction.

As aforesaid, the temperature of the reaction can vary widely. However,the preferred range is between 0° C. and the boiling point of thereaction system, with 10° C. to 40° C. being most preferred. It ispreferred to carry out the reaction at atmospheric pressure. Althoughhigher or lower pressures can be used if desired, no advantage in theuse of the more extreme conditions is evident. The reaction usuallytakes several hours to complete at about room temperature andatmospheric pressure, after which the polyamine can be separated fromthe solvent and catalyst by known means such as evaporation andfiltration. The polyamine products are clear liquids which have littleodour and do not impart objectionable colour to cured resins.

These curing agents or hardeners find particular utility for curableepoxy adhesive compositions used for adhering together a variety ofmaterials including metal, plastics, glass, and ceramics to formstructural components or laminated articles, and are applicable to epoxyresins of widely varying molecular weights and viscosities. Themetal-to-metal adhesive bonds achieved by these curing agents exhibitshear and bond strengths superior to those of many conventional epoxyadhesives. Typical useful epoxy resins are those prepared fromepichlorohydrin and polyhydroxy compounds, particularly bisphenol-A. Inaddition to these glycidyl polyethers, the hardeners are useful withmixed polyethers containing olefinic unsaturation, e.g. the allylglycidyl mixed diether of bisphenol-A. Also, other polyhydric alcohols,polyfunctional halohydrins and polyepoxides are useful and include suchcompounds as alpha and beta dichlorohydrin, butadiene dioxide,diglycidyl ether, resorcinol, hydroquinone, pyrocatechol,phloroglucinol, bisphenol-F, dihydroxy biphenyl, dihydroxy diphenylsulphone, ethylene glycol, erythritol and glycerol. More completelistings of useful epoxy resins appear in U.S. Pat. Nos. 2,817,644 and2,633,458. As stated in those specifications and as applicable to thepresent invention, the useful polyepoxides have an "epoxide equivalency"greater than one and preferably are those possessing per averagemolecule at least two epoxide ##STR4## groups which preferably areterminal, i.e. ##STR5## groups. The term "epoxide equivalency" refers tothe number of ##STR6## groups, determined by established analyticaltechniques, contained in the average molecular weight of the polyepoxideconcerned. The polyepoxides may be saturated or unsaturated, aliphatic,cycloaliphatic, aromatic or heterocyclic and may be substituted ifdesired with substituents such as chlorine atoms, hydroxyl groups, andether radicals, and may be monomeric or polymeric.

The amount of hardener to be used depends on the type of epoxy resin,the curing rate desired, the curing conditions, and other factors. Forexample, from 14 to 35% by weight of hardener per total weight of resinplus hardener would be useful in ordinary epoxy resin systems. As shownin Table 1 below, a useful range of hardener for the particular resinemployed therein in parts by weight based on total parts by weight ofresin plus hardener of 100, is indicated to be from 16 to 30, or more.The most effective amount of hardener for any particular resin system,and its application, including curing temperature considerations, arereadily ascertainable by those skilled in the art.

The following examples illustrate a specific preparation of a polyamineof the present invention and its use as a curing agent. These examplesare illustrative only, however, and are not to be construed as limitingthe invention in any manner.

EXAMPLE I 1,3-Bis(4-Aminomethylcyclohexylmethylamino)propan-2-ol

A solution of 2.0 g of sodium hydroxide in 5 ml of water was added to astirred solution of 14.2 g. of 1,4-cyclohexanebis(methylamine) (CHBMA)in 100 ml of methanol. The mixture was cooled in ice and maintained at atemperature of 10° C. during a dropwise addition of 4.63 g. ofepichlorhydrin over a period of 10 minutes. The reaction mixture wasstirred for 12 hours while allowing the temperature to equilibrate to20° C. over this period. A small quantity (about 1.4 g.) of sodiumchloride was removed by filtration. The reaction mixture was furtherheated to reflux and stirred for 2 hours and about 1.2 g. of sodiumchloride was separated by filtration. The methanol was then completelyevaporated from the reaction mixture using a rotary evaporator to leavea colourless oil product weighing 17.0 g. Infra-red and N.M.R. analysisconfirmed the structure of the product as1,3-bis(4-aminomethylcyclohexylmethylamino)propan-2-ol, hereinafterreferred to as BACMP.

EXAMPLE II Evaluation of Curing Agents in Adhesive Applications

For all the comparative evaluations an epoxy resin AY 150 sold byCiba-Geigy and based on the diglycidyl ether of bisphenol-A was used. Inthese evaluations, the curing effectiveness, measured as average load atbond failure (Table 2), of triethylene tetramine (TETA), CHBMA, and thepresent BACMP in the above resin were compared. The formulations testedare given in Table 1 below, wherein each of the formulation groupsA-D-H, B-E-I and C-F-J contained substantially equimolar amounts of thecompared hardeners. Formulation G is an isolated example and shows theeffect of too little BACMP hardener.

Each test specimen was prepared from two panels of mild steel measuring4 inches by 1 inch by about 0.02 inch (101.6 mm by 25.4 mm by about 0.5mm) (as in ASTM D1002-64), each of which was abraded on one side usingcarborundum powder, washed and dried. The panels were degreased bysuspension in trichloroethylene vapour for two hours, and were then airdried. The adhesive formulations were prepared by mixing the resin andhardener by hand in shallow aluminium pans to permit dissipation ofheat. Each formulation was then applied to one surface of a panel and ajoint was made by overlapping another panel half an inch (12.7 mm) overthe adhesive. The overlapped portions were then clamped together undermoderate pressure (about 210 g/cm²) and each specimen was heated at 100°C. for 20 minutes in a thermostatically controlled fan-oven. Thespecimens were then allowed to cool and stand overnight before testing.

Each specimen was placed in an Instron Tensile Tester with 1 inch (25.4mm) of each end gripped by the jaws such that the long axis of thespecimen coincided with the direction of applied pull through the centreline of the jaw assembly. The loading was applied at a free crossheadspeed of 2 mm/minute. In Table 2, the average load at failure in Kg./cm²of bond area, and the nature of this failure (cohesion or adhesion) isrecorded for each specimen, which was tested at least in duplicate.

                  TABLE 1                                                         ______________________________________                                        Formulations (Parts/Weight)                                                              A   B     C     D   E   F   G   H   I   J                          ______________________________________                                        Epoxy Resin  88    91    94  74  78  82  88  80  84  88                       (Ciba Geigy AY105)                                                            TETA         12     9     6  --  --  --  --  --  --  --                       BACMP        --    --    --  26  22  18  12  --  --  --                       CHBMA        --    --    --  --  --  --  --  20  16  12                       ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                      Average                                                         Adhesive      Load at    Nature of                                            Formulation   Bond Failure                                                                             Bond Failure                                         ______________________________________                                        A (TETA)      387        Adhesion                                             B (TETA)      385        Adhesion                                             C (TETA)      310        Cohesion                                             D (BACMP)     443        Adhesion                                             E (BACMP)     475        Adhesion                                             F (BACMP)     475        Adhesion                                             G (BACMP)     135        Cohesion                                             H (CHBMA)     410        Adhesion                                             I (CHBMA)     415        Adhesion                                             J (CHBMA)     400        Adhesion                                             ______________________________________                                    

The invention has been described in considerable detail with particularreference to certain preferred embodiments thereof but it will beunderstood that variations and modifications can be effected within thespirit and scope of the invention.

We claim:
 1. A method of curing an epoxy resin wherein there is used ascuring agent a compound having the structure ##STR7## wherein R, R¹, R²and R³ are each independently selected from hydrogen and straight orbranched chain alkyl groups of 1 to 10 carbons, and such groupssubstituted with 1-3 of the same or different groups selected fromalkoxy of 1-10 carbons, phenyl, cyclohexyl and hydroxyl.
 2. A laminatedstructure having its component members bonded together at theirinterfaces by an epoxy resin containing as a curing agent at least onecompound as claimed in claim
 1. 3. A laminated structure according toclaim 2 wherein R is --H.